/*
 * Copyright 2019 The gRPC Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.grpc.xds.internal.security.trust;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Strings;
import com.google.re2j.Pattern;
import io.envoyproxy.envoy.extensions.transport_sockets.tls.v3.CertificateValidationContext;
import io.envoyproxy.envoy.type.matcher.v3.RegexMatcher;
import io.envoyproxy.envoy.type.matcher.v3.StringMatcher;
import java.net.Socket;
import java.security.cert.CertificateException;
import java.security.cert.CertificateParsingException;
import java.security.cert.X509Certificate;
import java.util.Collection;
import java.util.List;
import java.util.Locale;
import javax.annotation.Nullable;
import javax.net.ssl.SSLEngine;
import javax.net.ssl.SSLParameters;
import javax.net.ssl.SSLSocket;
import javax.net.ssl.X509ExtendedTrustManager;
import javax.net.ssl.X509TrustManager;

/**
 * Extension of {@link X509ExtendedTrustManager} that implements verification of
 * SANs (subject-alternate-names) against the list in CertificateValidationContext.
 */
final class XdsX509TrustManager extends X509ExtendedTrustManager implements X509TrustManager {

  // ref: io.grpc.okhttp.internal.OkHostnameVerifier and
  // sun.security.x509.GeneralNameInterface
  private static final int ALT_DNS_NAME = 2;
  private static final int ALT_URI_NAME = 6;
  private static final int ALT_IPA_NAME = 7;

  private final X509ExtendedTrustManager delegate;
  private final CertificateValidationContext certContext;

  XdsX509TrustManager(@Nullable CertificateValidationContext certContext,
                      X509ExtendedTrustManager delegate) {
    checkNotNull(delegate, "delegate");
    this.certContext = certContext;
    this.delegate = delegate;
  }

  private static boolean verifyDnsNameInPattern(
      String altNameFromCert, StringMatcher sanToVerifyMatcher) {
    if (Strings.isNullOrEmpty(altNameFromCert)) {
      return false;
    }
    switch (sanToVerifyMatcher.getMatchPatternCase()) {
      case EXACT:
        return verifyDnsNameExact(
            altNameFromCert, sanToVerifyMatcher.getExact(), sanToVerifyMatcher.getIgnoreCase());
      case PREFIX:
        return verifyDnsNamePrefix(
            altNameFromCert, sanToVerifyMatcher.getPrefix(), sanToVerifyMatcher.getIgnoreCase());
      case SUFFIX:
        return verifyDnsNameSuffix(
            altNameFromCert, sanToVerifyMatcher.getSuffix(), sanToVerifyMatcher.getIgnoreCase());
      case CONTAINS:
        return verifyDnsNameContains(
            altNameFromCert, sanToVerifyMatcher.getContains(), sanToVerifyMatcher.getIgnoreCase());
      case SAFE_REGEX:
        return verifyDnsNameSafeRegex(altNameFromCert, sanToVerifyMatcher.getSafeRegex());
      default:
        throw new IllegalArgumentException(
            "Unknown match-pattern-case " + sanToVerifyMatcher.getMatchPatternCase());
    }
  }

  private static boolean verifyDnsNameSafeRegex(
          String altNameFromCert, RegexMatcher sanToVerifySafeRegex) {
    Pattern safeRegExMatch = Pattern.compile(sanToVerifySafeRegex.getRegex());
    return safeRegExMatch.matches(altNameFromCert);
  }

  private static boolean verifyDnsNamePrefix(
      String altNameFromCert, String sanToVerifyPrefix, boolean ignoreCase) {
    if (Strings.isNullOrEmpty(sanToVerifyPrefix)) {
      return false;
    }
    return ignoreCase
        ? altNameFromCert.toLowerCase(Locale.ROOT).startsWith(
            sanToVerifyPrefix.toLowerCase(Locale.ROOT))
        : altNameFromCert.startsWith(sanToVerifyPrefix);
  }

  private static boolean verifyDnsNameSuffix(
          String altNameFromCert, String sanToVerifySuffix, boolean ignoreCase) {
    if (Strings.isNullOrEmpty(sanToVerifySuffix)) {
      return false;
    }
    return ignoreCase
            ? altNameFromCert.toLowerCase(Locale.ROOT).endsWith(
                sanToVerifySuffix.toLowerCase(Locale.ROOT))
            : altNameFromCert.endsWith(sanToVerifySuffix);
  }

  private static boolean verifyDnsNameContains(
          String altNameFromCert, String sanToVerifySubstring, boolean ignoreCase) {
    if (Strings.isNullOrEmpty(sanToVerifySubstring)) {
      return false;
    }
    return ignoreCase
            ? altNameFromCert.toLowerCase(Locale.ROOT).contains(
                sanToVerifySubstring.toLowerCase(Locale.ROOT))
            : altNameFromCert.contains(sanToVerifySubstring);
  }

  private static boolean verifyDnsNameExact(
      String altNameFromCert, String sanToVerifyExact, boolean ignoreCase) {
    if (Strings.isNullOrEmpty(sanToVerifyExact)) {
      return false;
    }
    return ignoreCase
        ? sanToVerifyExact.equalsIgnoreCase(altNameFromCert)
        : sanToVerifyExact.equals(altNameFromCert);
  }

  private static boolean verifyDnsNameInSanList(
      String altNameFromCert, List<StringMatcher> verifySanList) {
    for (StringMatcher verifySan : verifySanList) {
      if (verifyDnsNameInPattern(altNameFromCert, verifySan)) {
        return true;
      }
    }
    return false;
  }

  private static boolean verifyOneSanInList(List<?> entry, List<StringMatcher> verifySanList)
      throws CertificateParsingException {
    // from OkHostnameVerifier.getSubjectAltNames
    if (entry == null || entry.size() < 2) {
      throw new CertificateParsingException("Invalid SAN entry");
    }
    Integer altNameType = (Integer) entry.get(0);
    if (altNameType == null) {
      throw new CertificateParsingException("Invalid SAN entry: null altNameType");
    }
    switch (altNameType) {
      case ALT_DNS_NAME:
      case ALT_URI_NAME:
      case ALT_IPA_NAME:
        return verifyDnsNameInSanList((String) entry.get(1), verifySanList);
      default:
        return false;
    }
  }

  // logic from Envoy::Extensions::TransportSockets::Tls::ContextImpl::verifySubjectAltName
  private static void verifySubjectAltNameInLeaf(
      X509Certificate cert, List<StringMatcher> verifyList) throws CertificateException {
    Collection<List<?>> names = cert.getSubjectAlternativeNames();
    if (names == null || names.isEmpty()) {
      throw new CertificateException("Peer certificate SAN check failed");
    }
    for (List<?> name : names) {
      if (verifyOneSanInList(name, verifyList)) {
        return;
      }
    }
    // at this point there's no match
    throw new CertificateException("Peer certificate SAN check failed");
  }

  /**
   * Verifies SANs in the peer cert chain against verify_subject_alt_name in the certContext.
   * This is called from various check*Trusted methods.
   */
  @VisibleForTesting
  void verifySubjectAltNameInChain(X509Certificate[] peerCertChain) throws CertificateException {
    if (certContext == null) {
      return;
    }
    List<StringMatcher> verifyList = certContext.getMatchSubjectAltNamesList();
    if (verifyList.isEmpty()) {
      return;
    }
    if (peerCertChain == null || peerCertChain.length < 1) {
      throw new CertificateException("Peer certificate(s) missing");
    }
    // verify SANs only in the top cert (leaf cert)
    verifySubjectAltNameInLeaf(peerCertChain[0], verifyList);
  }

  @Override
  public void checkClientTrusted(X509Certificate[] chain, String authType, Socket socket)
      throws CertificateException {
    delegate.checkClientTrusted(chain, authType, socket);
    verifySubjectAltNameInChain(chain);
  }

  @Override
  public void checkClientTrusted(X509Certificate[] chain, String authType, SSLEngine sslEngine)
      throws CertificateException {
    delegate.checkClientTrusted(chain, authType, sslEngine);
    verifySubjectAltNameInChain(chain);
  }

  @Override
  public void checkClientTrusted(X509Certificate[] chain, String authType)
      throws CertificateException {
    delegate.checkClientTrusted(chain, authType);
    verifySubjectAltNameInChain(chain);
  }

  @Override
  public void checkServerTrusted(X509Certificate[] chain, String authType, Socket socket)
      throws CertificateException {
    if (socket instanceof SSLSocket) {
      SSLSocket sslSocket = (SSLSocket) socket;
      SSLParameters sslParams = sslSocket.getSSLParameters();
      if (sslParams != null) {
        sslParams.setEndpointIdentificationAlgorithm("");
        sslSocket.setSSLParameters(sslParams);
      }
    }
    delegate.checkServerTrusted(chain, authType, socket);
    verifySubjectAltNameInChain(chain);
  }

  @Override
  public void checkServerTrusted(X509Certificate[] chain, String authType, SSLEngine sslEngine)
      throws CertificateException {
    SSLParameters sslParams = sslEngine.getSSLParameters();
    if (sslParams != null) {
      sslParams.setEndpointIdentificationAlgorithm("");
      sslEngine.setSSLParameters(sslParams);
    }
    delegate.checkServerTrusted(chain, authType, sslEngine);
    verifySubjectAltNameInChain(chain);
  }

  @Override
  public void checkServerTrusted(X509Certificate[] chain, String authType)
      throws CertificateException {
    delegate.checkServerTrusted(chain, authType);
    verifySubjectAltNameInChain(chain);
  }

  @Override
  public X509Certificate[] getAcceptedIssuers() {
    return delegate.getAcceptedIssuers();
  }
}
